The present invention relates to an improved positional sensing transducer of the type shown in U.S. Pat. No. 3,958,203, issued May 18, 1976 in the name of Victor M. Bernin and assigned to the assignee of the present invention. The transducer utilizes an elongated tube constructed of a magnetically saturable material. A sense wire runs through the tube and a pair of oppositely poled magnets are positioned on diametrically opposite exterior portions of the tube so that the magnetic flux from the magnets will completely saturate the portion of the tube that lies between the magnets, while the remaining portion of the tube remains unsaturated.
The Bernin patent uses a hollow, elongated cylindrical tube constructed of a material which is magnetically saturable, a sense wire that runs through the tube, and two oppositely poled magnets that move along the outside of the tube in order to provide an accurate linear indication of the position of the magnets with respect to the tube on the sense line. In other words, the present invention does not provide a "1" or a "0" output signal, but instead it may be used to accurately determine the position of the saturating magnets with respect to the tube. The portion of the elongated tube that lies between the magnets is saturated while the remaining portion is not. Because the tube provides a closed flux path, there is no substantial fringing affect at the ends of the saturating magnets; and, therefore, the portion of the tube that is not between the magnets remains substantially unsaturated. Since the output signal that is provided on the sense wire through the tube is not dependent upon the magnetic characteristics of the tube, but merely upon the position of the magnets with respect to the tube, a very linear output signal is achieved. In addition, problems that affect magnetic sensors that depend on partial saturation of the sensing element, such as temperature variation and aging variation, are also eliminated. Moreover, magnetic force that is required to operate the device of the present invention is not critical because of reliance on saturation of the tube between the magnets to produce the output signal.